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Already solved the #4TechChallenge for this month? Here’s a bonus question to keep your mind in challenge mode:

Why do no prime numbers have digits that sum to 15?


Post your methods and solutions in the comments below and look out for the answers next month.

If you are someone who enjoys problem-solving, logical thinking and technology, check out our Forensic Technology graduate page or professional roles to see if they are the right fit.

What's the answer?

For those of you that had a crack at the bonus question our justification is here:

Deliotte_BonusQ-FT-Answer

If you've enjoyed this quiz, have a look at this Forensic Technology Challenge and keep your eye on the blog for more quizzes to come.

Comments

  • Any number that has digits that sum to 15 must be divisible by 3 (this is because 100, 10 and 1 are all equivalent to 1 mod 3). Therefore any number with digits summing to 15 must be divisible by 3, and so cannot be prime.

    Posted by: Daniel on 16/07/2016

  • Thanks for the reply Daniel!

    Can you provide a bit more detail for your justification? What about if the digits sum to 18 or 21 etc....?

    Posted by: James (Deloitte) on 20/07/2016

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